As a disc recording medium on which, for example, digital data such as a high-quality digital video signal is optically recorded, a playback-only DVD (digital versatile disc or digital video disc) has been broadly known. Moreover, as disc recording media which enable writing once or rewriting by using the DVD format, a DVD-R (DVD-recordable), a DVD-RW (DVD-rewritable) and a DVD-RAM (DVD-random access memory) are being popularized.
Furthermore, a next-generation optical disc is to be commercialized which can realize a large capacity of approximately more than 23 gigabytes with a track pitch of 0.32 μm, a scanning density of 0.12 μm/bit and a diameter of 120 mm, by using a combination of a blue laser beam with a wavelength of 405 nm and an objective lens with NA of 0.85. With respect to this next-generation optical disc, a recording layer is formed on a substrate, and a transparent cover layer with a thickness of approximately 0.1 mm is formed on the recording layer. The transparent cover layer has an excellent optical characteristic and it is hard-coated so as to be scratch-proof, for example. The laser beam is cast onto the recording layer via the transparent cover layer having the above-described thickness of 0.1 mm.
By reducing the thickness of the transparent cover layer, the spot diameter of the laser beam on the recording layer can be reduced. However, if the spot diameter is thus reduced, the optical disc becomes more susceptible to a dust particle of a size which would not cause any problem when the spot diameter is large.
Therefore, in the case of recording data onto the next-generation optical disc with a thin transparent cover layer, reinforcement of an error correcting code is necessary. This also applies to a BCA (burst cutting area) on an optical disc where the disc ID is recorded, as well as a data area where content data is recorded.
However, if the error correcting code in the BCA is to be reinforced, the redundancy is increased and the quantity of recordable data is reduced.
On the other hand, if the redundancy is reduced, the error correction capability is lowered.